1. Technical Field
Several aspects of the present invention relate to a method of manufacturing a semiconductor device and a semiconductor device, and in particular to a technology for forming a metal oxide having a cubic, tetragonal, or orthorhombic crystal structure.
2. Related Art
Reduction of device size is effective for improving performance of existing MOS transistors, and therefore, reduction of gate insulating film thickness as well as reduction of gate length has been promoted. However, the silicon oxide film, which has been used as the gate insulating film in the past, has reached a limit of thickness, and it has been getting difficult to prevent the leakage current from the gate electrode. In order for solving this problem, a gate insulating film material with high permittivity has been getting necessary, and as such a material, hafnium oxide such as HfSiOx or HfAlOx is now under review.
Incidentally, hafnium oxide easily crystallizes at relatively low temperature, and therefore, in the form of a thin film, there are pointed the problems of surface roughness caused by crystal grains and increase in the leakage current flowing through the boundary of the crystal grains (see e.g., S. Kremmer, et al., J. Appl. Phys. 97, 074315 (2005)).
Further, hafnium oxide has a permittivity varying depending on the crystal structure, and generally forms a monoclinic crystal structure having a low permittivity by a thermal treatment. In contrast, there is a case of realizing a cubic or tetragonal crystal structure having a high permittivity by mixing zirconium (Zr), yttrium (Y), silicon (Si), or the like with hafnium oxide (see e.g., K. Kita, et al., Appl. Phys. Lett. 86, 102906 (2005), K. Tomida, et al., Appl. Phys. Lett. 89, 142902 (2006), D. H. Triyoso, et al., SISC, P-4 (2006)). Further, there is a case of eliminating voids in the hafnium oxide by executing an annealing treatment on the hafnium oxide covered with a TiN film, thereby improving the flatness thereof (see e.g., D. Triyoso, et al., SISC, P-4 (2006)).
However, in these technologies known to the public, it is required to mix the elements (hereinafter also referred to as impurities) other than hafnium oxide such as Zr, Y, or Si for obtaining the hafnium oxide with a cubic, tetragonal, or orthorhombic crystal structure, and there has never been a technology capable of forming the hafnium oxide with a cubic, tetragonal, or orthorhombic crystal structure without mixing the impurities.